Carbon content measurement in a basic oxygen furnace

ABSTRACT

A system for controlling the operation of a basic oxygen furnace in response to measurements of the carbon loss through the exhaust gases and the oxygen flow rate to the lance. The carbon content of the bath as determined from the carbon loss rate and the measured oxygen flow rate as well as the calculated bath temperature provide a basis for controlling the furnace. Oxygen flow is maintained constant until silicon is removed and is then increased at a steady maximum rate. Simultaneously, the lance is brought down as slag buildup occurs. Oxygen flow is modified by a positive feedback signal responsive to carbon loss rate and is limited when carbon loss rate changes rapidly. Also, lance height is modified in response to rate of change of oxygen flow. The oxygen is then shut off and the lance raised when the carbon content of the bath, as determined from carbon loss rate divided by oxygen flow, is at a desired value and the temperature of the bath is also at a desired value.

United States Patent [151 3,640,119

Blnm et al. 5] Feb. 8, 1972 [54] CARBON CONTENT MEASUREMENT 3,463,6318/1969 Vagssiere et al ..75/60 IN A BASIC OXYGEN FURNACE Bernard Blum,Buffalo, N.Y.; John W. Schwartzenberg, Maple Glen, Pa.

Leeds & Northrup Company, Philadelphia, Pa.

Filed: May 6, 1970 Appl. No.: 34,936

Inventors:

Assignee:

Related US. Application Data Division of Ser. No. 534,617, Feb. 14,1966, Pat. No. 3,528,800, which is a continuation-in-part of Ser. No.479,867, Aug. 16, 1965, abandoned.

US. Cl ..73/23, 23/255 E, 75/60,

References Cited UNITED STATES PATENTS 7/1967 Onta et al. ..73/23 XPrimary Examiner-Richard C. Queisser Assistant Examiner-C. E. Snee,1llAttamey william G. Miller, Jr. and Raymond F. MacKay 1 1 ABSTRACT Asystem for controlling the operation of a basic oxygen furnace inresponse to measurements of the carbon loss through the exhaust gasesand the oxygen flow rate to the lance. The carbon content of the bath asdetermined from the carbon loss rate and the measured oxygen flow rateas well as the calculated bath temperature provide a basis forcontrolling the furnace. Oxygen flow is maintained constant untilsilicon is removed and is then increased at a steady maximum rate.Simultaneously, the lance is brought down as slag buildup occurs. Oxygenflow is modified by a positive feedback signal responsive to carbon lossrate and is limited when carbon loss rate changes rapidlyv Also, lanceheight is modified in response to rate of change of oxygen flow. Theoxygen is then shut off and the lance raised when the carbon content ofthe bath, as detennined from carbon loss rate divided by oxygen flow, isat a desired value and the temperature of the bath is also at a desiredvalue.

5 Claims, 4 Drawing Figures mzman mi 81912 3.640.119

SHEET 1 OF 3 FIG. 1

FIG. 1A FIG. 1B

1s sea e00 804 l MEASUR'NG AND 22 M -RETRANSMITTER FIG. 2

mvmrores BERNARD BLUM JOHN W. SCHWARTZENBERG BY l m )7 M AGENT CARBONCONTENT MEASUREMENT IN A BASIC OXYGEN FURNACE CROSS-REFERENCE TO RELATEDAPPLICATION This application is a division of application Ser. No.534,617 filed Feb. 14, 1966, now US. Pat. No. 3,528,800, which was filedas a continuation-in-part of application Ser. No. 479,867, Aug. 16,1965, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to apparatus forproviding a measuring system for determining the carbon content of thebath of an oxygen-blown, steel-refining vessel, particularly in the lowcarbon region toward the end of a heat.

In the process of refining pig iron to produce steel in a basic oxygenfurnace, high-purity oxygen is introduced at a high velocity through alance positioned above the bath in the furnace so that the oxygenimpinges upon the surface of the bath. The high-purity oxygen combineswith the impurity elements in the bath including the carbon, manganese,phosphorus and silicon as well as iron itself. By this process ofcombination the oxides of the impurity elements are formed. The oxidesof carbon are evolved as gases while the other oxides are retained in aslag cover over the molten metal bath.

It is usually desired that the refining process be carried out until aparticular percentage of carbon remains in the molten metal and thetemperature of the molten metal is at a predetermined point. When thecarbon content and the temperature are at the desired values, theprocess can be terminated. Thus, in using this process it is importantto have an accurate measure of the carbon content of the bath during thefinal portion of the refining process when the carbon content is at alow value.

In carrying out this invention there is provided means for measuring therate at which the carbon is removed from the bath by the generation of asignal whose magnitude is representative of the concentration of carboncontaining gases in the exhaust gas recovery system of the refiningvessel and means are provided which are responsive to that signal forindicating carbon content in the bath. When the oxygen supplied to thevessel is variable, the last-named means may include means for measuringthe rate of flow of oxygen into the vessel and means for establishingthe ratio between the rate of carbon removal and the rate of oxygenflow. That ratio is representative of the efficiency of carbon removalfrom the bath and that ratio has been found to be indicative of thecarbon content of the bath at low carbon values.

It is an object of this invention to provide an improved means formeasuring the carbon content in the bath of a basic oxygen furnace.

It is a further object of this invention to provide a means fordetermining the carbon content of the bath of a basic oxygen furnaceduring the final portion of the heat in order to determine the time atwhich the heat has been completed.

For a complete description of this invention, reference should be madeto US. Pat. No. 3,528,800 and more specifically to that portion of thespecification starting at column 4, line 36 continuing to column 20,line 65. Particular reference with regard to the invention should bemade to that portion of the specification found at column 18, line 67continuing to column 19, line 57.

What is claimed is:

l. A measuring system for establishing a signal indicative of the carboncontent of the bath in an oxygen-blown furnace comprising means forestablishing from analysis of the exhaust gases of said furnace a signalindicative of the carbon loss rate of the furnace bath,

means for establishing a signal indicative of the flow of oxygen to thelance of said furnace, and

means for dividingsaid carbon loss signal by said oxygen flow signal. 2.A measuring system for determining the carbon content remaining in thebath of a basic oxygen furnace toward the 5 end of a low carbon heatcomprising means for producing a first signal indicative of the rate ofloss of carbon from the furnace,

means for producing a second signal indicative of the oxygen flow rateinto said furnace,

means responsive to the ratio of said first to said second signal toproduce a third signal indicative of the existing carbon removalefficiency of the heat, and

indicator means including a substantially logarithmic scale formeasuring and indicating the carbon content of said bath.

3. A measuring system for measuring the carbon content of the bath in abasic oxygen furnace comprising means for producing a first signalrepresentative of the concentration of carbon containing gases in theexhaust system of said furnace,

means for producing a second signal representative of the rate of flowof the gases in the exhaust system,

means for multiplying said first and said second signal to produce athird signal indicative of the carbon loss rate from said furnace,

means for producing a fourth signal representative of the rate of oxygenflow to the lance of said furnace,

means for introducing said fourth signal into a lagging network toobtain a lagged fourth signal, means for producing from said laggedfourth signal a signal indicative of the carbon equivalent of saidoxygen flow,

means for dividing said carbon equivalent signal into said third signalto produce a signal indicative of the existing carbon removalefficiency, said carbon removal efficiency being related to the carboncontent of said bath when said carbon content is low, and

indicating means having a substantially logarithmic scale in terms ofcarbon content connected to respond to said carbon removal efficiencysignals to provide an indication of the carbon content of said bath.

4. A system for determining the efficiency of carbon removal from thebath of an oxygen-blown, steel-refining vessel comprising means formeasuring the rate at which carbon is removed from the bath,

means for measuring the rate of flow of oxygen blown into said vessel,and

means for establishing the ratio between the rate of carbon removal andthe rate of oxygen flow, said ratio being representative of theefficiency of carbon removal from said bath.

5. A system for determining the efficiency of carbon removal from thebath of an oxygen-blown, steel-refining vessel comprising means formeasuring the rate at which carbon is removed from the bath including;

means for measuring the concentration of carbon-containing gases in theexhaust gas recovery system into which the gas leaving said refiningvessel are drawn,

means for measuring the rate of flow of gases in said exhaust gasrecovery system, and

means for multiplying said concentration of carbon-containing gases bysaid rate of flow of gases in said exhaust gas recovery system toproduce a measure of the rate at which carbon is being removed from saidbath;

means for measuring the rate of flow of oxygen blown into said vessel;and

means for establishing the ratio between the rate of carbon removal andthe rate of oxygen flow, said ratio being representative of theefiiciency of carbon removal from said bath.

2. A measuring system for determining the carbon content remaining inthe bath of a basic oxygen furnace toward the end of a low carbon heatcomprising means for producing a first signal indicative of the rate ofloss of carbon from the furnace, means for producing a second signalindicative of the oxygen flow rate into said furnace, means responsiveto the ratio of said first to said second signal to produce a thirdsignal indicative of the existing carbon removal efficiency of the heat,and indicator means including a substantially logarithmic scale formeasuring and indicating the carbon content of said bath.
 3. A measuringsystem for measuring the carbon content of the bath in a basic oxygenfurnace comprising means for producing a first signal representative ofthe concentration of carbon containing gases in the exhaust system ofsaid furnace, means for producing a second signal representative of therate of flow of the gases in the exhaust system, means for multiplyingsaid first and said second signal to produce a third signal indicativeof the carbon loss rate from said furnace, means for producing a fourthsignal representative of the rate of oxygen flow to the lance of saidfurnace, means for introducing said fourth signal into a lagging networkto obtain a lagged fourth signal, means for producing from said laggedfourth signal a signal indicative of the carbon equivalent of saidoxygen flow, means for dividing said carbon equivalent signal into saidthird signal to produce a signal indicative of the existing carbonremoval efficiency, said carbon removal efficiency being related to thecarbon content of said bath when said carbon content is low, andindicating means having a substantially logarithmic scale in terms ofcarbon content connected to respond to said carbon removal efficiencysignals to provide an indication of the carbon content of said bath. 4.A system for determining the efficiency of carbon removal from the bathof an oxygen-blown, steel-refining vessel comprising means for measuringthe rate at which carbon is removed from the bath, means for measuringthe rate of flow of oxygen blown into said vessel, and means forestablishing the ratio between the rate of carbon removal and the rateof oxygen flow, said ratio being representative of the efficiency ofcarbon removal from said bath.
 5. A system for determining theefficiency of carbon removal from the bath of an oxygen-blown,steel-refining vessel comprising means for measuring the rate at whichcarbon is removed from the bath including; means for measuring theconcentration of carbon-containing gases in the exhaust gas recoverysystem into which the gas leaving said refining vessel are drawn, meansfor measuring the rate of flow of gases in said exhaust gas recoverysystem, and means for multiplying said concentration ofcarbon-containing gases by said rate of flow of gases in said exhaustgas recovery system to produce a measure of the rate at which carbon isbeing removed from said bath; means for measuring the rate of flow ofoxygen blown into said vessel; and means for establishing the ratiobetween the rate of carbon removal and the rate of oxygen flow, saidratio being representative of the efficiency of carbon removal from saidbath.